An ultrasonic diagnostic apparatus is conventionally known as a medical image diagnostic apparatus. An ultrasonic diagnostic apparatus is configured to generate an image inside an object using ultrasonic waves, and a medical image interpretation specialist, such as a medical doctor or radiologist, interprets the generated image inside the object.
In the present specification, an ultrasonic image which was imaged in the past by an ultrasonic diagnostic apparatus and used as a reference is referred to as a “reference image” and an ultrasonic image to be generated in an examination performed from now on is referred to as a “live image”. In the field of an ultrasonic diagnostic apparatus, a method of simultaneously displaying a reference image and a live image has been studied. For instance, a method has been studied, in which a three-dimensional image, which has been already imaged, based on three-dimensional image data is treated as a reference image and is displayed together with a live image corresponding to the reference image.
Here, when ultrasonic imaging is conducted using a contrast agent in the contrast mode, special transmission and reception of ultrasonic wave are used to obtain only the echoes caused by the contrast agent, while tissue signals are canceled. In other words, tissue structure is not depicted in a contrast-enhanced image generated in the contrast mode. Thus, alignment of a live image to be generated in the contrast mode and a reference image in which tissue structure is not depicted is difficult, because characteristics of any tissue structure are not depicted in both images.